FIG. 1 is a schematic block diagram 100 of the electrical and optical components of a prior art coherent optical transceiver. Skew can be introduced in the traces between elements as well as within each element. It would be advantageous for each element to compensate for skew.
In dual-polarization coherent communication, there are at least four signal paths from the digital signal processor (DSP) to the output optical signal. These are the in-phase and quadrature modulator inputs for X- and Y-input optical polarizations. X- and Y-polarizations are orthogonal polarizations in the input optical fiber. In such a scenario, it is important that the relative timing skew between each of these signal paths from the DSP to the output optical signal is kept as low as possible. There is skew between X- and Y-polarizations, as well as between the In-phase and Quadrature components of a signal within a certain polarization. These are called XY and IQ timing skews, respectively. Similarly, there are four such paths from the incoming optical signal to the DSP. There can be both XY and IQ timing skew in the transmitter and in the receiver.
There is a need for improved systems and methods for correcting skew.